A study is proposed which will first define the morphological characteristics of hitherto ill-defined ganglion and amacrine cells of the cat retina using three techniques; Golgi-impregnations, single cell marking of neurons with horseradish peroxidase (HRP), and back filling of ganglion cells via HRP injections in the optic nerve. An understanding of the morphologies of the cell types is essential before an analysis of their synaptic circuitry can be attempted. Serial section analysis of the cat area centralis will be continued and reconstructions of portions of neurons will be compared with their light microscopic counterparts. Physiologically identified cells, stained with HRP, will be examined directly by electron microscopy and an analysis of their input/output relationships with other neurons ascertained. From cytological recognition criteria for many of the bipolar and amacrine cells, new cell types evaluated by these methods can be assigned roles in the rod and cone pathways, or in the ON and OFF center channels through the retina. An understanding of the functional architecture of the cat area centralis is thought to be applicable to the central retina of the monkey, for most of the cell types are similar in morphology and the neural pathways are basically the same. Additional studies on: 1) the monkey outer plexiform layer are proposed which may result in an understanding of the color inputs to the horizontal cells and 2) turtle ganglion cells may allow us to understand the morphology and neural circuitry of orientation sensitivity. Linking neural circuitry of the vertebrate retina with functional pathways will contribute to our knowledge of the organization of the visual message relayed to the higher visual centers.